1. Field of the Invention
The present invention relates generally to a fibre channel (FC) communication system that may be used in a in a data storage system to facilitate exchange of data and commands among I/O controllers and mass storage devices, and more specifically, to such a communication system wherein the controllers and the mass storage devices are coupled to each other via a plurality of configurable FC loops.
2. Brief Description of Related Prior Art
Network computer systems generally include a plurality of geographically separated or distributed computer nodes that are configured to communicate with each other via, and are interconnected by, one or more network communications media. One conventional type of network computer system includes a network storage subsystem that is configured to provide a centralized location in the network at which to store, and from which to retrieve data. Advantageously, by using such a storage subsystem in the network, many of the network's data storage management and control functions may be centralized at the subsystem, instead of being distributed among the network nodes.
One type of conventional network storage subsystem, manufactured and sold by the Assignee of the subject application (hereinafter “Assignee”) under the tradename Symmetrix™ (hereinafter referred to as the “Assignee's conventional storage system”), includes a plurality of disk mass storage devices (e.g., disk drives) configured as one or more redundant arrays of independent (or inexpensive) disks (RAID). The disk devices are controlled by disk controllers (commonly referred to as “back end” controllers/directors) that may communicate (i.e., exchange data and commands) with the disk devices via Small Computer System Interface (SCSI) protocol communication channels. The disk controllers are coupled via a bus system to a shared cache memory resource in the subsystem. The cache memory resource is also coupled via the bus system to a plurality of host controllers (commonly referred to as “front end” controllers/directors). The disk controllers are coupled to respective disk adapters that, among other things, interface the disk controllers to the disk devices. Similarly, the host controllers are coupled to respective host channel adapters that, among other things, interface the host controllers via channel input/output (I/O) ports to the network communications channels (e.g., SCSI, Enterprise Systems Connection (ESCON), or FC based communications channels) that couple the storage subsystem to computer nodes in the computer network external to the subsystem (commonly termed “host” computer nodes or “hosts”).
In the Assignee's conventional storage system, the disk devices are grouped together into respective sets, and each set of disk devices may be controlled by respective pair of disk controllers. If one of the disk controllers in the respective pair fails, the other (i.e., redundant) disk controller in the pair may assume the duties of the failed disk controller, and thereby permit the set of disk devices to continue to operate, despite the failure of the failed disk controller.
Also in the Assignee's conventional storage system, the disk devices are placed in respective housings and stored in one or more chassis. The chassis may include a multiplicity of sets of slots for receiving respective housings within which the respective disk devices are placed. The chassis may also include an electrical back plane having a multiplicity of electromechanical connectors. The connectors may be mated with respective electromechanical connectors of the housings to electrically and mechanically couple the disk devices to the chassis.
In general, two types of commercially-available disk devices may be mounted in the chassis used in the Assignee's conventional storage system: “low profile” and “half-high” form factor disk devices. With the exception of their respective heights, a low profile form factor disk device (hereinafter “LP device”) may have identically the same dimensions as a half-high form factor disk device (hereinafter “HH device”). An LP device may have a height of 1 inch; an LP device may have a height of 1.6 inches.
At present, the storage capacity of a HH device may be approximately twice that of an LP device. However, the speed with which data may be read from or written to an HH device may be slower than the speed with which data may be read from or written to an LP device.
Only two types of chassis may be used in the Assignee's conventional storage system. One type of chassis is configured to receive and mount only LP devices, and the other type of chassis is configured to receive and mount only HH devices. Thus, in the Assignee's conventional storage system, a single chassis cannot contemporaneously receive and store both LP and HH devices; instead, all of the disk devices stored in a single chassis must have a single form factor (i.e., LP or HH).
This is unfortunate, since, given the above-described relative differences in the capabilities of HH and LP devices, in certain practical applications of a data storage system, it may be desirable to employ in an individual chassis combinations of both HH and LP devices that, when taken together, may permit the overall performance of the system to be improved. Also unfortunately, since an individual chassis used in the Assignee's conventional data storage system is unable to receive and store disk devices having multiple different form factors, this inherently reduces the design flexibility of the data storage system.
Additionally, it has been proposed to replace the SCSI communication channels that permit communication among the disk devices and disk controllers with FC protocol communication channels, in order to increase the speed with which communication between the disk devices and disk controllers may be effected. According to this proposal, each such FC communication channel comprises a serial, unidirectional, communication ring or loop system. In order to provide for redundancy failover in the event of failure of a disk controller (i.e., in order to permit a respective set of disk devices to continue to be used despite the failure of one disk controller in the respective disk controller pair that control the set of disk devices, as discussed above), the set of disk devices may be coupled to the redundant disk controller in the disk controller pair, using a separate, independent, FC communication ring or loop system. Thus, two respective FC communication loop systems may be provided for each set of disk devices.
As a result of the topology and serial nature of the communication permitted using such an FC loop system, if any node in the loop system fails or becomes inoperative, the entire loop system becomes inoperative. Thus, for example, if the disk controller, the disk adapter coupled to the disk controller, or any of the disk drives coupled to an FC loop system fails or becomes inoperative, then the continuity of loop system is broken (i.e., open), and the loop system becomes inoperative. This may result in the data stored in the entire set of disk devices becoming unavailable unless and until all inoperative and/or failed nodes in the loop system are repaired or replaced with operative nodes.
One technique that has been proposed to solve this problem involves using loop resiliency circuit switches (hereinafter “LRCS”) that enable failed or inoperative nodes to be removed from the loop system. In one proposed arrangement that uses such switches, a respective printed circuit board (hereinafter “PCB”) is provided for each respective disk device. Each PCB has a respective pair of LRCS, one of which is coupled to one of the respective FC loop systems that is coupled to the respective disk device, and the other of which is coupled to the other of these loop systems. By appropriately controlling the states of these switches, an inoperative or failed disk device may be bypassed so as to close a loop system that become open or broken as a result of the failure or inoperability of the disk device. Unfortunately, if one LRCS in a respective pair of LRCS fails, the entire PCB having the pair of LRCS must be replaced; this may result in disruption of the loop systems that were coupled to the PCB, and thereby, may result in disruption of the entire data storage system.
One technique that has been proposed to solve this problem involves coupling a respective PCB to each of the two respective FC loop systems that are coupled to a set of disk drives. Each such PCB includes a respective set of n LRCS (wherein “n” is the number of disk devices in the respective set of disk devices). A back plane is used to interconnect the two PCB, associated selectors or multiplexers, and the disk devices. Unfortunately, in order to provide the serial, or sequential, FC connections necessary to implement this arrangement, it has been proposed to utilize an elaborate, complex fan-out back plane wiring arrangement.
Additional examples of FC arrangements are disclosed in e.g., Eli Leshem, U.S. Pat. No. 5,729,763, and Van Cruyningen, World Intellectual Property Organization Publication No. WO 99/26146, published May 27, 1999.
Accordingly, it would be desirable to provide an FC communication system that (1) may be used in conjunction with a mass storage device mounting system that may utilize a single type of chassis that is able to contemporaneously receive and store disk mass storage devices that have different form factors (e.g., both HH and LP devices), (2) may facilitate communication among disk controllers and such disk devices, and (3) may provide communication fault tolerance in the event of, among other things, failure of a disk controller and/or one or more disk devices, without requiring the elaborate, complex fan-out back plane wiring arrangement of the prior art.